The present invention relates generally to a pair of trial spectacles and, in particular, to a pair of spectacles for testing the feeling and effect of various kinds of ophthalmic lenses at the time of wearing so that a wearer with a reduced power of accommodation can test whether multifocal lenses are suitable prior to constructing an actual pair of spectacles and lenses for permanent use.
Multifocal lenses for use in spectacles or eyeglasses may include a bifocal lens, a double bifocal lens, a trifocal lens, a progressive multifocal lens or the like. These respective multifocal lenses include various lenses designed for use by a wearer having a reduced power of accommodation. Such lenses prove convenient for wearers with a reduced power of accommodation since such a wearer can see both far and near objects clearly with a single lens. However, such types of multifocal lenses have several shortcomings. For example, a wearer may experience a jumping of image at the dividing line between the various lenses of the bifocal and trifocal lenses and may also experience shaking and blurring of the image in the peripherial portion of the progressive multifocal lens.
It proves difficult for a wearer to fully understand and appreciate the optical characteristics of the types of multifocal lenses under discussion when only an oral or written explanation of the effects and shortcomings of the lenses is made. Thus, it often happens that the wearer cannot realize the above-described shortcomings until the wearer actually tries a pair of spectacles constructed to meet his particular optical specifications and requirements. A wearer may think that he could understand the optical characteristics by explanation and agrees that a pair of spectacles having multifocal lenses should be made, but finds that he cannot endure the shortcomings of the spectacles and lenses when he actually receives and wears the pair of spectacles. Once having been constructed to the wearer's particular optical prescription and the wearer finds the multifocal lenses in the pair of spectacles unsuitable for him, such pair of spectacles and lenses cannot be utilized for other wearers having different optical prescriptions and requirements.
It is therefore desirable for a wearer to wear a pair of spectacles having multifocal lenses on a trial basis in order to understand its characteristics through his own experience before constructing the actual pair of spectacles and lenses for permanent use by the wearer. Trial spectacle frames and trial lenses have been conventionally used in order for a user to wear them on a trial basis. However, heretofore, the main object of utilizing the trial frames and lenses was to allow the wearer's ophthalmologist or optometrist to determine the focal power of the ophtalmic lenses necessary for that particular wearer. Accordingly, the aperture of trial lenses is relatively small in order to reduce the weight thereof even when three or four lenses, for example, are overlapped in the trial frame, since it is sufficient that only the central front view can be seen by the wearer. The effective diameters of trial lenses utilized in trial spectacle frames are generally less than 35 mm. In this regard, see Moss, A Demonstration Kit for Progressive Addition Lenses, Review of Optometry/May, 1978.
However, in the case of multifocal lenses, the portion of the lens for near vision is generally positioned below the center of the lens. In the progressive multifocal lenses, shaking of the image and blur distinctly appear not in the center of the lens but in the peripheral portions thereof. Thus, in the case of testing the feeling and effect of various kinds of multifocal lenses at the time of wearing, it is difficult for a user to understand the optical characteristics of the multifocal lenses even by utilizing the conventional trial frame and trial lenses whose aperture is small, since an important portion of the lens for understanding the optical characteristics of the multifocal lenses is not available in convention trial lenses. In addition, in the case of using multifocal lenses, it proves most important to adjust the fixed point or "fitting point" on the lens, which is generally at or near the optical center of the lens, with the center of the wearer's pupil.
Thus, when a wearer is looking at distant objects, it is necessary that the fitting point of the lens acccurately coincide with the center of the wearer's pupil in a front view. Accordingly, a trial frame for testing needs to have the function where the lens can be horizontally and vertically adjusted. In addition, since conventional trial frames are heavy, they will tend to slip down the wearer's nose or the wearer will feel uncomfortable because of the weight of the pair of spectacles. It is therefore difficult for a wearer to accurately judge whether a pair of spectacles having multifocal lenses are right for him since he cannot accurately judge the feeling at the time of wearing. In addition, as the conventional trial lenses do not have any means for accurately showing the position of the fitting point, an accurate adjustment cannot be made.
Accordingly, a pair of trial spectacles which allows a wearer to test whether a pair of spectacles having multifocal lenses is suitable, which provides the same characteristics as an actual pair of spectacles with multifocal lenses is desired.